I have a penpal I’ve been writing weekly to for the better part of a year.
I liked writing to him, we’d talk about books and music and fandom stuff and I thought we got on fairly well. But since a couple months ago he’s started to stop writing about the more personal stuff and has pretty much only been writing about US politics. I get that Trump is a big isssue for him as a non-citizen living in the US, but as someone who doesn’t live there, I neither know or care enough to talk very much in depth about the issue. I tried to change the subject by asking about his personal life, but all I got in my last letter were somewhat curt answers on that regards but a four paragraph spiel about the Black Panthers and the FBI. I mean, the guy went to Paris a couple weeks back. You’d think he’s want to talk about that a little bit.

If we were talking in real life, he’d grasp that I want to change the subject, but I’m not sure how to put out that message via writing. Especially when I was technically the one to bring up it up in the first place. I essentially like him as a friend; how can I subtly get him to stop talking about his favorite subject matter without hurting our friendship?

Remind him there are many subjects more scintillating than this, apologize for bringing it up and for exacerbating his anxieties, give him other subjects or return to current conversation one for which you both share much enthusiasm.

As gently as I can, I’m going to say that as a friend, I try to listen to the anxieties that my friends have. It’s usually no fun, but it’s part of being a friend. Telling him that you don’t want to talk about something that affects him deeply… there’s no way to do that without hurting the friendship. For him this is personal stuff.

So, your choices are:
* Ask questions about the things that he’s concerned about.
* Tell him bluntly that you don’t want to talk about politics, but only if you’re prepared to lose the friendship.
* Only answer the parts of the letter that you are interested in, and don’t include politics in your own letters.

I agree with @maryrobinette — if you don’t want to participate in the political conversation aspect of your pen pal’s letter, do not respond to that portion. Focus on keeping your letters on the topics you two had previously enjoyed. Hopefully, he will start seeing your letters as a break from his fears and anxieties and re-engage on topics that you both enjoy.